isPositiveGain - should use double instead of int

[Sciss]

LinKernighanTSP/src/LinKernighan.java

Line 320 in 55b6056

int gain = 0;

I think this is a bug, because getDistance returns double precision and somehow the java compiler doesn't complain about gain += getDistance(t2, t3) - getDistance(t1,t2); even though here is a loss of precision. For example, with wi29.tsp I get a slightly better path when changing to double.